Slot antenna mounted within openwork support tower



July 23, 1968 A. ALFORD 3,394,377

SLOT ANTENNA MOUNTED WITHIN OPENWORK SUPPORT TOWER Filed March 30, 1965FIG! INVENTOR ANDREW ALFORD ATTORNEYS United States Patent 3,394,377SLOT ANTENNA MOUNTED WITHIN OPENWORK SUPPORT TGWER Andrew Alford,Winchester, Mass. (299 Atlantic Ave., Boston, Mass. 02110) Filed Mar.30, 1965, Ser. No. 443,907 5 Claims. (Cl. 343767) ABSTRACT OF THEDISCLOSURE The present invention relates in general to electromagneticenergy transduction and more particularly concerns a novel slottedcylinder mounted within a triangular tower and coacting with the towerto form a mechanically rugged compact radiating system havingsubstantially omnidirectional radiation characteristics in thehorizontal plane. The invention is especially useful in connection withradiating UHF television signals at great heights and coacting with anumber of similarly mounted slotted cylinders appropriately fed to forma high gain radiation system etficiently directing energy toward thedesired listening area from a mechanically rugged structure capable ofwithstanding severe weather conditions.

The transmission range of UHF television signals is normally limited toapproximately line of sight. Accordingly, range is maximized by locatingthe transmitting antenna as high as practical while efiicientlyilluminating the desired listening area with sufficient energy. Sincethe attenuation of UHF energy a8 a function of distance from theradiator is greater than that of VHF energy, achieving a given qualityof television reception over a given area requires more effectiveradiated power at UHF than is required at VHF. Since raising the actualtransmitter power is costly and limited by practical considerations,raising effective radiated power to desired levels at UHF isadvantageously accomplished by using high gain antennas. Although highgain may be achieved by using multi-element antennas, serious mechanicalproblems are introduced when it is desired to support a heavymulti-element antenna at the great heights normally desired forsatisfactory television coverage.

The nature of the problem will be better appreciated when it isrecognized that stacking twelve or more elements over a twelve or morewavelength height at the top of a mast may be required to obtain thedesired gain. Such a mast sufficient to support the multi-element loadwould have dimensions large enough to interfere with the radiationcharacteristics of the radiating elements.

Accordingly, it is an important object of this invention to provide UHFelectromagnetic transduction means that is mechanically rugged and maycomprise a large number of individual stacked radiating elements toachieve high gain in a rugged mechanical assembly at great heights.

It is another object of the invention to achieve the preceding objectwith a relatively compact structure eX- hibiting substantiallyomnidirectional radiation characteristics in the horizontal plane.

According to the invention, a slotted cylindrical radiating element issituated within a skeletal triangular tower much nearer to one of thethree supporting posts than the others with the slot facing away fromthe said one supporting post so that the slotted cylindrical radiatorcoacts with the tower to provide a radiation pattern that is essentiallyomnidirectional in the 'horizontal plane;

Numerous other features, objects and advantages of the invention willbecome apparent from the following specification when read in connectionwith the acc0mpanying drawing in which:

FIG. 1 is a perspective view of a slotted cylinder in a triangular towersection embodying the principles of the invention; and

FIG. 2 is a graphical representation of the omnidirectional radiationcharacteristic of the embodiment of FIG. 1 when dimensioned foroperation at 1000- megacycles.

With reference now to the drawing and more particularly to FIG. 1thereof, there is shown a perspective view of an embodiment of theinvention. Only a single section of a tower of triangular cross sectionis shown so as not to obscure the principles of the invention. Acomplete tower comprises a number of such sections cascaded whichsections are essentially similar. Thus, a typical triangular towersection will include vertical poles 11, 12 and 13 joined together byupper horizontal bars 14, 15 and -16 by lower horizontal bars 17, 18 and19 and by cross struts 21, 22 and 23. A ladder 24 is mounted adjacent tovertical pole 12 to provide access for servicing a radiating element.The slotted cylindrical radiator 25 is supported closely adjacent topole 11 with its vertical slot 26 (FIG. 2) facing away from vertical.pole 11 and including the plane that perpendicularly bisects horizontalbars 15 and 18. Antenna 25 is shown fed at the bottom by a coaxialtransmission line 27. The slotted cylindrical radiator is preferably ofthe type disclosed in Alford US. Patent No. 2,611,867.

When a number of radiating elements are stacked and fed by anappropriate arrangement of coaxial cables, it is preferred that thecoaxial cables rise vertically closely adjacent to the vertical polefurthest from the radiating element 25 and the ladder 24. For astructure comprising a stacked array of sections like that shown in FIG.1 this vertical pole would be pole 13. It is also preferred that thespecific feeder to the bottom of a radiating element be dressed closelyalong a horizontal strut to the element feedpoint from the verticalpole, typically along strut 19 from vertical pole 13.

A large number of like slotted cylinders may be located one above theother at the top of the radiating tower at two wavelength intervals toprovide increased gain. By appropriately controlling the relative phaseof energy applied to the different elements, the vertical directivity ofan array of elements may be control-led in accordance with knownprinciples. The radiating structure thus formed is characterized by highradiation efiiciency, desired directivity, high gain and mechanicalruggedness. By locating the antenna within the triangular tower severestresses caused by heavy wind loading are relatively loW and deicing orother weather protective apparatus may be conveniently added to theslotted cylindrical radiator without detracting from the desiredmechanical or electrical characteristics of the apparatus. Still anotherfeature of the invention resides in the convenient and relatively safeaccess for servicing, for practical towers may be made which permitservice personnel to function from the inside of the tower supported bytemporary platforms which may be laid on the struts.

Referring to FIG. 2, there is shown the radiation pattern in thehorizontal plnae of the structure illustrated in FIG. 1 with thediameter of the vertical poles 11, 12 and 13 1% inches, with theseparation between adjacent vertical poles 22 /2 inches, with theseparation between slotted cylindrical antenna 25 and vertical pole 111.46 inches, and with slotted cylinder 25 having a slot a little lessthan two wavelengths long, about 4 wavelength 3 wide and the cylinderdiameter being about wavelength e M. a H

The specific embodiment described herein is by way of example only. Itis evident that those skilled in the art may now make numerousmodifications of and departures from the specific embodiment describedherein without departing from the inventive concepts. Consequently, theinvention is to be construed as limited solely by the spirit and scopeof the appended claims.

What is claimed is: 1. Electromagnetic transduction apparatuscomprising, means defining a supporting tower of triangular crosssection comprising three vertical conducting membersat the vertices ofthe triangular cross section interconnected and supported by supportinglinks, conducting means defining only a single verticalradiating slot inany one horizontal plane, means for supporting said conducting meanswith said slot generally parallel to and inside of said vertical membersand much closer to one of said members than the others with saidvertical slot separated from said one member by an electrically opaqueportion of said conducting means, said conducting means coacting withsaid supporting tower to provide a radiation characteristic in thehorizontal plane that is substantially omnidirectional. 2.Electromagnetic transduction apparatus in accordance with claim 1wherein said conducting means defining a vertical radiating slotcomprises means defining a conducting cylindrical surface formed withvertical radiating slot embracing the plane perpendicularly bisecting afirst side plane between said others of said members and passing throughsaid one member,

a portion of said conducting cylindrical surface being between said slotand said one member.

3. Electromagnetic transduction apparatus in accordance with claim 2wherein said supporting tower is of equilateral triangular crosssection.

4. Electromagnetic transduction apparatus in accordance with claim 3wherein said supporting tower comprises three upper horizontal links,three lower horizontal links and three diagonal links with each diagonallink extending diagonally upward from near the junction of a respectivelower horizontal link with a respective vertical member near thejunction of a respective upper horizontal link with a vertical memberadjacent to said respective vertical member.

5. Electromagnetic transduction apparatus in accordance with claim 4 andfurther comprising,

a ladder section immediately adjacent to a ladder-adjacent one of saidvertical members adjacent to said one vertical member which ladder isparallel to the plane joining said ladder-adjacent one of said verticalmembers and said one vertical member.

References Cited UNITED STATES PATENTS 2,611,867 9/1952 Alford 3437702,771,606 11/ 1956 Kandoian 343890 3,254,343 5/1966 Laub et a1 343890FOREIGN PATENTS 832,564 4/1960 Great Britain. 1,122,510 5/1956 France.

ELI LIEBERMAN, Primary Examiner.

